1. Field of the Invention
The present invention relates to liquid jet heads, liquid jet apparatuses, and piezoelectric elements.
2. Description of the Related Art
A known piezoelectric element used in a liquid jet head is constituted of, for example, a pair of electrodes and a piezoelectric layer held between these electrodes.
For example, a ferroelectric with a perovskite crystal structure is used for the piezoelectric layer (piezoelectric thin film) constituting the piezoelectric element. The piezoelectric thin film is formed by, for example, forming a piezoelectric precursor film on the lower electrode by the sol-gel process and firing the piezoelectric precursor film, as disclosed in, for example, Japanese Unexamined Patent Application Publication No. 2001-274472.
The piezoelectric layer thus formed shows considerable variations in, for example, crystal conditions, such as crystal grain size, due to differences in production conditions, and also shows variations in surface roughness due to the variations in crystal conditions. This piezoelectric layer has a problem in that a crack can occur in the piezoelectric layer during the driving of the piezoelectric element, depending on the crystal conditions of the piezoelectric layer. The inventors have found that the problem of cracking has some correlation with the relationship between the surface roughness of the lower electrode constituting the piezoelectric element and the surface roughness of the piezoelectric layer.
This problem arises not only in piezoelectric elements mounted on liquid jet heads, such as ink jet recording heads, but also in piezoelectric elements mounted on other devices.